Explain the periodic properties of elements and their reactivity trends in the periodic table.

(N/A) Periodic Trends and Reasons:
- Across a period (left to right),atomic radius and ionic radius decrease.
- Consequently,ionization enthalpy increases,and electron gain enthalpy becomes more negative.
- Elements on the extreme left (Alkali metals) have a high tendency to lose electrons,while elements on the extreme right (Halogens) have a high tendency to gain electrons.
- Reactivity is generally higher at the extremes and lower in the middle of the periodic table.
Periodic Properties in Periods:
$(1)$ Redox Reactivity: Elements on the extreme left are strong reducing agents,while those on the extreme right are strong oxidizing agents.
$(2)$ Metallic and Non-metallic Properties: Metallic character decreases and non-metallic character increases from left to right.
$(3)$ Reactivity with Oxygen: Elements at the extremes readily form oxides.
- Oxides of elements on the extreme left are most basic (e.g.,$Na_{2}O$).
- Oxides of elements on the extreme right are most acidic (e.g.,$Cl_{2}O_{7}$).
- Oxides of elements in the center are amphoteric (e.g.,$Al_{2}O_{3}, As_{2}O_{3}$) or neutral (e.g.,$CO, NO, N_{2}O$).
- Amphoteric oxides react with both acids and bases,while neutral oxides show neither property.
$(4)$ Transition elements are metals but are less electropositive than group-$1$ and group-$2$ elements.